1. Field of the Invention
The present invention relates to a detection apparatus applicable to a medical diagnostic imaging apparatus, a non-destructive testing apparatus, an analysis apparatus using radiation, or the like, and also relates to a radiation detection apparatus and a radiation detection system equipped with a radiation detection apparatus.
2. Description of the Related Art
In recent years, advances in semiconductor technology have enabled the mass production of large-sized radiation sensors. The semiconductor building blocks of a modern radiation sensor (radiation detection apparatus) include a conversion element such as a photoelectric conversion element and a switch element such as a thin film transistor (TFT). To form a radiation detection apparatus such as a medical X-ray detection apparatus, these semiconductor building blocks may be combined with a fluorescent member (scintillator) and arranged in one- or two-dimensional arrays of pixels that perform wavelength conversion, i.e., convert radiation such as an X-ray into visible light or the like.
In general, the pixel structure used in the radiation detection apparatus can be classified into two types, i.e., a single-plane type in which a conversion element and a switch element are disposed in the same plane and a stacked type in which a conversion element is disposed above a switch element. In the production of the single-plane type, the conversion element and the switch element can be produced using the same semiconductor production process, which allows simplification of the production process. In the case of the stacked-type detection apparatus, the provision of the conversion element above the switch element makes it possible to increase the size of the conversion element in each pixel compared with the single-plane type. Therefore, the stacked-type detection apparatus is capable of providing a larger signal, a higher signal-to-noise ratio, and a higher sensitivity than can be provided by the single-plane type detection apparatus.
In radiation detection apparatuses, in particular in medical X-ray detection apparatuses, there is a need for a reduction in the amount of radiation a patient is exposed to. To meet this requirement, it is important to achieve a sensor having higher sensitivity and high signal-to-noise (S/N) ratio. In a sensor, noise is generated by many sources. Devices/elements that can be noise sources include conversion elements, switch elements, signal lines, integrating amplifiers, and peripheral circuits. Hereinafter, noise generated by a signal line will be referred to as signal line noise. When a signal line has parasitic capacitance C, the signal line noise is given by a following equation.signal line noise=√kTcHereinafter, noise generated by an integrating amplifier will be referred to as amplifier noise. In a case where an integrating amplifier with feedback capacitance Cf is used as a charge reading amplifier, the amplifier noise is given by the following equation.amplifier noise=C/Cf×noise at amplifier inputTherefore, a reduction in parasitic capacitance C of the signal line is effective to reduce noise of the detection apparatus. That is, to achieve high sensitivity, it is effective to reduce noise by reducing the parasitic capacitance of the signal line.
In the detection apparatus, there is also a need for an increase in driving speed. When a driving line via which a driving pulse is supplied to control turning-on/off of a switch element has capacitance Cg and resistance Rg, the time constant τ of this driving line is given by the following equation.τ=Cg×Rg Thus, if the capacitance and/or the resistance of the driving line increases, the time constant τ of the driving line increases, which can cause a driving pulse transmitted via the driving line to become dull or distorted. Therefore, if the turn-on period of the switch element is reduced, the dullness can make it difficult for the switch element to be in an on-state for a designed necessary period. That is, the dullness makes it difficult to reduce the turn-on period, which makes it difficult to increase the driving speed.
Japanese Patent Laid-Open No. 2002-76360 discloses a technique to realize a single-plane type radiation detection apparatus with signal/driving lines (hereinafter, referred to simply as lines) having reduced resistance. U.S. Patent Application Publication No. 2007/0045556 proposes a technique to reduce resistance of a line in a stacked type radiation detection apparatus.
In conventional radiation detection apparatuses, therefore, there is a need for a reduction in pixel pitch, an increase in the number of pixels, an increase in sensitivity, and an increase in driving speed regardless of whether the pixel structure in these radiation detection apparatuses is of the single-plane type or the stacked-type. In particular, since medical X-ray detection apparatuses include various types of detection apparatuses such as an X-ray mammography apparatus, an X-ray transmission detecting apparatus capable of taking a moving image, etc., a reduction in pixel pitch and an increase in the number of pixels specific to each of these various types of medical X-ray apparatuses are highly desirable.